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OMC 190 overheating HELP

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Cymru95

New member
I recently bought a 1975 sea Ray boat with a OMC 190 engine (ford 302). I took it out for the first time and after about 10-15 minutes at high revs it overheated. It start smoking on the port side and disclosed/burnt the paint on the riser and also slightly disclosed the paint on the manifold. Also it burnt the paint around the spark plugs on the same size. I've taken the riser apart and it seems like it is clear of gunk but when I try to run it on the hose it heats up still on the upper side of the riser. On the opposite side of the engine the riser stays cool. So I presume that I need a new riser.

What really confuses me is why it heated up around the spark plugs, could it be the heat backing up from the riser or a compleatly separate issue. By this point I am complexity stuck with what to do.

as a side point the impeller is gone so I plan to replace that but I need to find out if I have solved the overheating issues first (don't want to burn out the impeller)
 
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OK here's a tip that will save you a lot of embarrassment and maybe your life. Don't take an unknown boat out into the water until you know everything's in good order. That means you put on the muffs and run it on the hard, or put it in the water at the ramp and run it while tied up at a dock. Go thru the gears and run it up to WOT and be sure there's nothing wrong.
It's a boat. you have to spend lots of money on it. Buy new manifolds and risers.
 
as a side point the impeller is gone so I plan to replace that but I need to find out if I have solved the overheating issues first (don't want to burn out the impeller)
Click to expand...

Ayuh,.... The Impeller is the 1st thing to change, in any over heat situation,.....

Start there, don't end there,....
 
Thanks for the comments - I'm going to ignore all comments that talk about what I should have done since that's not what I have asked for. (More to the point I did extensively test the boat on a hose connection prior to putting it in the water but since that by passes the impeller it's easy to miss an impeller problem) Also I'm not sure if one side was getting hotter before on the engine since it didn't overheat and FYI it still isn't overheating - I can now just tell that it is heading that way....

My biggest concern is why the area around the spark plugs heated up so much and if that was a knock on effect from the riser overheating. I don't have any signs of a blown head gasket.
 
If you can't get the hot water out, plugged riser, you can't get the cold water in. Riser's are first to go in old boats and your problem is a classic riser problem. I hope your engine isn't one of the Fords that you can't find manifolds for. I have searched high and low for a set for a customer. We'll keep our fingers crossed.
 
boatdoc55 said:
If you can't get the hot water out, plugged riser, you can't get the cold water in. Riser's are first to go in old boats and your problem is a classic riser problem. I hope your engine isn't one of the Fords that you can't find manifolds for. I have searched high and low for a set for a customer. We'll keep our fingers crossed.
Click to expand...

Thank you - a helpful reply! In terms of my risers they don't seem to be blocked, the water does only run around the bottom of the water jacket which I believe is the reason why it overheated on the top side. I plan to open up one of the other ports on the riser to manifold connection to allow better water flow. From what it seems like that is just a design flaw.

In in terms of the manifold, the water seems to be running though it but I'm going to take it off and blast water through it to remove any gunk that may have settled near the bottom of the manifold. Other than that there doesn't seem any other reason for it to overheat.

Can anyone suggest any other reason why the port bank of the engine would overheat? It runs perfectly with no backfires on all 8 cylinders. Oil seems ok, no leaks are apparent around the cylinder head.
 
If your risers are true risers and have the water flow up the front of it, across the top and then down and out, the top is where everyone of them plug. There is no cure but to acid dip them and this is becoming very hard to find someone to do it. I hope your style riser is still available. OMC did have a riser that fit both the Ford and Chevy but also made some one off ones. I would bet that one riser is shot and the other is close. Do the mani's have caps on the ends or are they the ones that are no longer available, no caps just nipples?
 
In spite of the fact that you came asking for advice, got some you didn't like and then acted like a tool, here's more. Ford 302s risers can be made to work no matter what. The fact that you may not be able to find the exact thing shouldn't be an issue. Osco makes a generic set that you can use and you can use cheap ebay silicone elbows to adapt them to your old y pipe. Done it, it works, and is an easy and elegant solution to unobtanium parts. The burnt heads may be fine assuming that the heads didn't warp when the thing overheated. Keep an eye on it.
 
My biggest concern is why the area around the spark plugs heated up so much and
Click to expand...

Ayuh,.... Because that area of the manifold is solid cast iron, no coolin' passages,....

It over heated because the impeller wasn't pushin' water into the motor,....
The hot side, ran outa what little water there was, 1st,....

Ya need to replace the impeller, 'n find All the missin' pieces,....
Then maybe it'll run alright,....
 
Not knowing how your boat is plumbed this is where I would start. If it's not fresh water cooled track down the outgoing coolant hoses, should be on the manifolds in the front. Disconnect those two hoses and start the engine either in a barrel or on the flusher. Start with a cold engine and you should be able to run it long enough to see if it's your impeller or if you have a blockage on the water going out. Lots of water should flow out the nipples on BOTH sides. If no water there than disconnect the one hose coming from the intermediate housing feeding the T-stat housing, water in. Start it again and if no water out that hose, as bondo says you get to replace the impeller. They're a pain on the old stringers but you have to do what you have to do.
 
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